where \(L_{cls}^{l}\)  and \(L_{reg}^{l}\)  are respectively the Focal loss [1]} and the \(L_1\)  loss.
\(\lambda _{1}\)  and \(\lambda _{2}\)  are coefficient to balance two terms, the superscript of \(L^{l}\)  denotes the conventional (legacy) loss in Siamese pair training paradigm [2]}.
